1. Field of the Invention
The present invention relates to a feedhorn, a radio wave receiving converter and an antenna, and particularly, to a feedhorn including a dielectric, a radio wave receiving converter and an antenna.
2. Description of the Background Art
Conventionally, an antenna for receiving a radio wave of satellite broadcasting or the like is known. To the antenna, a radio wave receiving converter is arranged. As a member constituting the radio wave receiving converter, a feedhorn in which a dielectric is connected to an open end of a waveguide is known (for example, see Japanese Patent Laying-Open No. 2001-217644).
According to Japanese Patent Laying-Open No. 2001-217644, a dielectric member constituted by a thick dielectric is fixedly connected to an open end of a waveguide. Such a dielectric member is manufactured using injection molding or the like.
However, the aforementioned dielectric member formed of a thick dielectric involves a problem that, when performing injection molding, a concave portion (a sinkmark generating portion) is generated at the outer portion thereof, or a bubble is generated in the inner portion thereof. Generation of such a concave portion or a bubble deteriorates the dimensional precision of the dielectric member.
Additionally, generation of such a concave portion or a bubble in the dielectric member also involves a problem that the radiation pattern characteristics of a feedhorn using the dielectric member is distorted (the radiation pattern characteristics deviate from the designed characteristics). As a result, the dielectric member with a concave portion or a bubble is treated as a defective, and thus becomes a cause of reducing yield of the dielectric member. Additionally, since a step of screening such a defective is required, the manufacturing period is prolonged. As a consequence, it has been one cause of increasing the manufacturing costs of the dielectric member (and hence, the feedhorn).